A number of methods and devices are believed to be understood for the contactless measurement of the profile depth of vehicle tires. In some of these methods, the measurement takes place on the dismounted tire, which is fastened rotatably in a special test stand. Other methods measure the profile depth of tires mounted on the vehicle. This may take place, on the one hand, by driving over a sensor installed in the floor or in a ramp. On the other hand, there are methods for measuring the profile depth on a roller type test stand. Finally, mobile handheld units are known for the profile measurement.
The documents U.S. Pat. Nos. 3,918,816, 5,245,867, 5,249,460 and EP 1 515 129 B1 discuss test stands for measuring the profile depth over the entire tread of a dismounted tire by sequential scanning of the tire tread, using a laser beam. For this, the tire has to be rotated in a controlled manner and the laser beam has to be shifted laterally mechanically.
Patent document DE 41 01 921 discusses a wheel balancing machine, with which the tread of a tire may be measured by a light section method. In this case, the dismounted tire has to be rotated as well.
Patent document DE 195 15 949 discusses the profile measurement over the complete tread of a dismounted tire by a stripe projection method. In this case, the tire is mounted on a rotational axis of a test stand, and rotated step-wise to a series of angular positions. A planar section of the tread is measured for each angular position. The tire has to be in an at-rest position for the taking of the image of each section, since a plurality of successive takes are required having different stripe illumination.
Patent document DE 1 809 459 discusses a light section method for measuring the profile depth during crossover. In this case, the profile depth is measured along a single line parallel to the rotational axis of the tire.
Patent document DE 43 16 984 discusses a method for measuring the profile depth during crossover. In this case, a triangulation sensor is shifted along a line transverse to the rolling direction of the tire.
Documents EP 0 469 948 B1, EP 1 952 092 B1 and U.S. Pat. No. 7,578,180 B2 discuss additional variants of triangulation methods for profile measurement during crossover.
Patent document WO 97/07380 A2 discusses the use of a light section method having one or more light sections for the measurement during crossover or in a roller set.
Patent document WO 96/10727 also discusses a triangulation method for measuring the profile depth on the vehicle. In addition to the profile measurement, an image-based visualization of the tire is suggested. For the illustration of a greater section of the tread, however, the tire has to be rotated in a roller set.
Patent document EP 0816799 A2 discusses, among other things, a variant in which the sensor is fastened to the vehicle and scans the tire during the movement of the vehicle. Triangulation methods, using laser scanners for profile measurement in a roller type test stand, are in DE 197 05 047 A1 and EP 1 394 503 B1.
Patent document DE 295 08 978 discusses a handheld laser measuring head for measuring the profile depth.
Patent document DE 10 2009 016 498 A1 discusses a method for ascertaining the profile depth of a vehicle tire, the tire being mounted on a vehicle on which the tire is rolled over the measuring station or stopped on it. The profile of the tire is optically scanned on at least one measuring line that is transverse to the rolling direction of the tire, a ray fan starting from a light source being reflected at the tire surface, and a signal of the reflected ray fan being picked up by a sensor and the signal of the reflected ray fan being evaluated using a triangulation method. In this context, the signal is picked up non-orthogonally to the tire surface.
What is common to all the methods named is that the profile depth is measured in each case along a single line or only on a small area of the tire tread, or that, for the measurement of a larger area of the tire tread, the wheel has to be dismounted, the vehicle has to be driven into a roller type test stand or the sensor has to be moved. Inspecting a greater area of the tread of the tire is therefore associated with increased effort.